Such a folding wheelchair is known, for example, from DE 297 24 574 U1. Via the cross-strut, the two side frames can be moved in relation to one another, essentially parallel to one another, between a use position, in which they are spaced apart, and a collapsed position, in which they are adjacent, and can be locked at least in the use position. The side frames, which comprise tubes which are welded to one another, have mounted on them, on the one hand, a respective rear drive wheel and, on the other hand, a respective caster wheel, which can be pivoted about a vertical axis. The cross-strut comprises tubes or connecting rods which cross over one another, are connected to one another at the crossover point in an articulated manner via a cross-strut joint and have their lower ends articulated in each case on a lower seat tube of the side frames.
In order for it to be possible, in the case of the folding wheelchair which is known from U.S. Pat. No. 8,449,032 B2, to adapt the seat surface of the folding wheelchair to potential users of different sizes, the seat depth is adjustable. In order to adjust the seat depth, the seat tubes are of telescopic design. The woven fabric forming the seat surface is positioned over the outer tube and connected to the inner tube. For telescoping purposes, the inner tube is pulled out of the outer tube and pulls along the woven fabric guided around the inner tube, and therefore the seat surface is increased in size. If the inner tube is pushed into the outer tube again, the woven fabric has to be positioned manually around the upper seat tube so that the seat surface does not form any creases, which can result in pressure marks on the user's body.
DE 297 18 536 U1 discloses a folding wheelchair in which, in order to adjust the seat depth, it is possible for the cross-strut, along with the seat accommodated thereon, to be displaced in the direction of travel of the wheelchair and to be fixed in at least two adjustment positions. In order for it to be possible to displace the cross-strut, screw-connections have to be released and then fixed securely again, and this makes it difficult for adaptation to the seat depth to be carried out quickly. Some kind of tool is usually also necessary for this purpose.
DE 202 21 587 U1 discloses a folding wheelchair in which the slit in the seat tube may be longer than the length of the woven seat fabric, and therefore the latter can be displaced in the forward and rearward direction in order for the seat depth to be adjusted. The seat tube is closed off by end caps. The woven seat fabric can be set in position by virtue of end caps of suitable length being selected.
In the case of the folding wheelchair which is described in U.S. Pat. No. 2,914,111, the woven seat fabric is provided with loops at its lateral ends, and a cover-retaining rod is accommodated in said loops. These are also used to fit the woven seat fabric into the slit seat tube. The seat tubes are closed via threaded end caps.